5A. Vertical alignment

Question 1

What is the equation for the length (L) of a vertical crest curve when the sight distance is less than the length?

Answer 1

AASHTO Chapter 3: 3-42

L = (AS^2) / (100 (sqrt(2h1) + sqrt(2*h2))^2

where:

L = length of vertical curve, ft
A = algebraic difference in grades, percent
S = sight distance, ft
h1 = height of eye above roadway surface, ft
h2 = height of object above roadway surface, ft

Question 2

What is the equation for the length (L) of a vertical crest curve when the sight distance is more than the length?

Answer 2

AASHTO Chapter 3: 3-42

L = 2S - (200 *sqrt(h1) + sqrt(h2))^2 / (A)

where:

L = length of vertical curve, ft
A = algebraic difference in grades, percent
S = sight distance, ft
h1 = height of eye above roadway surface, ft
h2 = height of object above roadway surface, ft

Question 3

What is K?

Answer 3

Rate of vertical curvature
K = L / A

L = length
A = algebraic difference in grades

Question 4

Where can the design control for vertical crest curves based on stopping distance be found

Answer 4

AASHTO Green Book: Chapter 3: Table 3-35

Question 5

Where can the design control for vertical crest curves based on passing sight distance be found

Answer 5

AASHTO Green Book: Chapter 3: Table 3-36